The present invention relates generally to methods for recombinant microbial production of fusion proteins and peptides derived from or based on Domain I (amino acids 17-45), Domain II (amino acids 65-99) and Domain III (amino acids 142-169) of bactericidal/permeability-increasing protein (BPI).
BPI is a protein isolated from the granules of mammalian polymorphonuclear leukocytes (PMNs or neutrophils), which are blood cells essential in the defense against invading microorganisms. Human BPI protein has been isolated from PMNs by acid extraction combined with either ion exchange chromatography [Elsbach, J. Biol. Chem., 254:11000 (1979)] or E. coli affinity chromatography [Weiss, et al., Blood, 69:652 (1987)]. BPI obtained in such a manner is referred to herein as natural BPI and has been shown to have potent bactericidal activity against a broad spectrum of gram-negative bacteria. The molecular weight of human BPI is approximately 55,000 daltons (55 kD). The amino acid sequence of the entire human BPI protein and the nucleic acid sequence of DNA encoding the protein have been reported in FIG. 1 of Gray et al., J. Biol. Chem., 264:9505 (1989), incorporated herein by reference. The Gray et al. DNA and amino acid sequences are set out in SEQ ID NOS: 264 and 265 hereto.
BPI is a strongly cationic protein. The N-terminal half of BPI accounts for the high net positive charge; the C-terminal half of the molecule has a net charge of -3. [Elsbach and Weiss (1981), supra.] A proteolytic N-terminal fragment of BPI having a molecular weight of about 25 kD has an amphipathic character, containing alternating hydrophobic and hydrophilic regions. This N-terminal fragment of human BPI possesses the anti-bacterial efficacy of the naturally-derived 55 kD human BPI holoprotein. [Ooi et al., J. Bio. Chem., 262: 14891-14894 (1987)]. In contrast to the N-terminal portion, the C-terminal region of the isolated human BPI protein displays only slightly detectable anti-bacterial activity against gram-negative organisms. [Ooi et al., J. Exp. Med., 174:649 (1991).] An N-terminal BPI fragment of approximately 23 kD, referred to as "rBPI.sub.23," has been produced by recombinant means and also retains anti-bacterial activity against gram-negative organisms [Gazzano-Santoro et al., Infect. Immun. 60:4754-4761 (1992)]. In that publication, an expression vector was used as a source of DNA encoding a recombinant expression product (rBPI.sub.23). The vector was constructed to encode the 31-residue signal sequence and the first 199 amino acids of the N-terminus of the mature human BPI, as set out in SEQ ID NOS: 264 and 265 taken from Gray et al., supra, except that valine at position 151 is specified by GTG rather than GTC and residue 185 is glutamic acid (specified by GAG) rather than lysine (specified by AAG). Recombinant holoprotein, also referred to as rBPI, has also been produced having the sequence set out in SEQ ID NOS: 264 and 265 taken from Gray et al., supra, with the exceptions noted for rBPI.sub.23. An N-terminal fragment analog designated rBPI.sub.21, or rBPI.sub.21.DELTA.cys has been described in co-owned, copending U.S. Pat. No. 5,420,019 which is incorporated herein by reference. This analog comprises the first 193 amino acids of BPI holoprotein as set out in SEQ ID NOS: 264 and 265 but wherein the cysteine at residue number 132 is substituted with alanine, and with the exceptions noted for rBPI.sub.23.
The bactericidal effect of BPI has been reported to be highly specific to gram-negative species, e.g., in Elsbach and Weiss, Inflammation: Basic Principles and Clinical Correlates, eds. Gallin et al., Chapter 30, Raven Press, Ltd. (1992). BPI is commonly thought to be non-toxic for other microorganisms, including yeast, and for higher eukaryotic cells. Elsbach and Weiss (1992), supra, reported that BPI exhibits anti-bacterial activity towards a broad range of gram-negative bacteria at concentrations as low as 10.sup.-8 to 10.sup.-9 M, but that 100- to 1,000-fold higher concentrations of BPI were non-toxic to all of the gram-positive bacterial species, yeasts, and higher eukaryotic cells tested at that time. It was also reported that BPI at a concentration of 10.sup.-6 M or 160 .mu.g/mL had no toxic effect, when tested at a pH of either 7.0 or 5.5, on the gram-positive organisms Staphylococcus aureus (four strains), Staphylococcus epidermidis, Streptococcus faecalis, Bacillus subtilis, Micrococcus lysodeikticus, and Listeria monocytogenes. BPI at 10.sup.-6 M reportedly had no toxic effect on the fungi Candida albicans and Candida parapsilosis at pH 7.0 or 5.5, and was non-toxic to higher eukaryotic cells such as human, rabbit and sheep red blood cells and several human tumor cell lines. See also Elsbach and Weiss, Advances in Inflammation Research, ed. G. Weissmann, Vol. 2, pages 95-113 Raven Press (1981). This reported target cell specificity was believed to be the result of the strong attraction of BPI for lipopolysaccharide (LPS), which is unique to the outer membrane (or envelope) of gram-negative organisms.
The precise mechanism by which BPI kills gram-negative bacteria is not yet completely elucidated, but it is believed that BPI must first bind to the surface of the bacteria through hydrophobic and electrostatic interactions between the cationic BPI protein and negatively charged sites on the bacterial LPS. Bacterial LPS has been referred to as "endotoxin" because of the potent inflammatory response that is stimulated i.e., the release of mediators by host inflammatory cells which may ultimately result in irreversible endotoxic shock. BPI binds to lipid A, reported to be the most toxic and most biologically active component of bacterial LPS.
In susceptible gram-negative bacteria, BPI binding is thought to disrupt LPS structure, leading to activation of bacterial enzymes that degrade phospholipids and peptidoglycans, altering the permeability of the cell's outer membrane, and initiating events that ultimately lead to cell death. [Elsbach and Weiss (1992), supra]. BPI is thought to act in two stages. The first is a sublethal stage that is characterized by immediate growth arrest, permeabilization of the outer membrane and selective activation of bacterial enzymes that hydrolyze phospholipids and peptidoglycans. Bacteria at this stage can be rescued by growth in serum albumin supplemented media [Mannion et al., J. Clin. Invest., 85:853-860 (1990)]. The second stage, defined by growth inhibition that cannot be reversed by serum albumin, occurs after prolonged exposure of the bacteria to BPI and is characterized by extensive physiologic and structural changes, including apparent damage to the inner cytoplasmic membrane.
Initial binding of BPI to bacterial LPS leads to organizational changes that probably result from binding to the anionic groups in the KDO region of LPS, which normally stabilize the outer membrane through binding of Mg.sup.++ and Ca.sup.++. Attachment of BPI to the outer membrane of gram-negative bacteria produces rapid permeabilization of the outer membrane to hydrophobic agents such as actinomycin D. Binding of BPI and subsequent gram-negative bacterial killing depends, at least in part, upon the LPS polysaccharide chain length, with long O-chain bearing, "smooth" organisms being more resistant to BPI bactericidal effects than short O-chain bearing, "rough" organisms [Weiss et al., J. Clin. Invest. 65: 619-628 (1980)]. This first stage of BPI action, permeabilization of the gram-negative outer envelope, is reversible upon dissociation of the BPI, a process requiring the presence of divalent cations and synthesis of new LPS [Weiss et al., J. Immunol. 132: 3109-3115 (1984)]. Loss of gram-negative bacterial viability, however, is not reversed by processes which restore the envelope integrity, suggesting that the bactericidal action is mediated by additional lesions induced in the target organism and which may be situated at the cytoplasmic membrane [Mannion et al., J. Clin. Invest. 86: 631-641 (1990)]. Specific investigation of this possibility has shown that on a molar basis BPI is at least as inhibitory of cytoplasmic membrane vesicle function as polymyxin B [In't Veld et al., Infection and Immunity 56: 1203-1208 (1988)] but the exact mechanism as well as the relevance of such vesicles to studies of intact organisms has not yet been elucidated.
In addition to its direct bactericidal activity, BPI is also capable of neutralizing the endotoxic properties of living or dead bacteria and LPS released from the bacteria. Because of its gram-negative bactericidal properties and its ability to bind to and neutralize bacterial LPS, BPI can be utilized for the treatment of mammals suffering from diseases caused by gram-negative bacteria, including bacteremia, endotoxemia, and sepsis. These dual properties of BPI make BPI particularly useful and advantageous for such therapeutic administration.
BPI protein products, including BPI-derived peptides, are useful as adjunct therapy with conventional antibiotics as described in copending and co-assigned U.S. patent application Ser. No. 08/311,611 filed Sep. 22, 1994 and WO95/08344 (PCT/US94/11225). Specifically, concurrent administration, or co-treatment, of such BPI protein products and an antibiotic or combination of antibiotics may improve the therapeutic effectiveness of antibiotics in a variety of ways, including by increasing susceptibility of gram-negative bacteria to a reduced dosage of antibiotics, by effectively reversing resistance of gram-negative bacteria to antibiotics, by providing synergistic or potentiating effects beyond the individual or additive effects of the BPI protein product or antibiotic alone, or by neutralizing endotoxin released by bacteria killed by antibiotics. Concurrent administration of BPI protein products and antibiotics provide unexpectedly superior therapeutic effects in vivo than either agent provides when administered alone. In particular, concurrent administration of BPI protein product according to this improved method of treatment is effective even when the gram-negative bacteria involved are considered to be resistant to the bactericidal effects of BPI protein product alone and/or antibiotic alone. BPI protein products are therefore useful for prophylaxis or treatment of gram-negative bacterial infections, including for prophylaxis of patients at high risk of gram-negative bacterial infection, e.g., patients who will undergo abdominal or genitourinary surgery, or trauma victims.
BPI protein products, including BPI-derived peptides, have been shown recently to have direct and indirect bactericidal and growth inhibitory effects on some gram-positive organisms as described in copending U.S. Patent Application Ser. No. 08/372,783 filed Jan. 13, 1995 and WO95/19180 (PCT/US95/00656). In addition, BPI protein products unexpectedly were shown to have the ability to increase the antibiotic susceptibility of gram-positive bacteria, including the ability to reverse in many instances the antibiotic resistance of gram-positive bacteria. BPI protein products and antibiotics provided additive and synergistic bactericidal/growth inhibitory effects when administered concurrently. Such BPI protein products are therefore useful for treating gram-positive bacterial infections, including conditions associated therewith or resulting therefrom (for example, sepsis or bacteremia).
BPI protein products, including BPI-derived peptides, have also been shown recently to have fungicidal/fungistatic effects as described in copending and co-assigned U.S. patent application Ser. No. 08/372,105 filed Jan. 13, 1995 and WO95/19179 (PCT/US95/00498). Such BPI protein products may be administered alone or in conjunction with known anti-fungal agents. When made the subject of adjunctive therapy, the administration of BPI protein products may reduce the amount of anti-fungal agent needed for effective therapy, thus limiting potential toxic response and/or high cost of treatment. Administration of BPI protein products may also enhance the effect of such agents, accelerate the effect of such agents, or reverse resistance of fungi to such agents.
BPI has other important biological activities. For example, BPI protein products, including BPI-derived peptides, have been shown to have heparin binding and heparin neutralization activities in copending and co-assigned U.S. Pat. No. 5,348,942 issued Sep. 20, 1994 incorporated by reference herein. These heparin binding and neutralization activities are significant due to the importance of current clinical uses of heparin. Heparin is commonly administered in doses of up to 400 U/kg during surgical procedures such as cardiopulmonary bypass, cardiac catherization and hemodialysis procedures in order to prevent blood coagulation during such procedures. When heparin is administered for anticoagulant effects during surgery, it is an important aspect of post-surgical therapy that the effects of heparin are promptly neutralized so that normal coagulation function can be restored. Currently, protamine is used to neutralize heparin. Protamines are a class of simple, arginine-rich, strongly basic, low molecular weight proteins. Administered alone, protamines (usually in the form of protamine sulfate) have anti-coagulant effects. When administered in the presence of heparin, a stable complex is formed and the anticoagulant activity of both drugs is lost. However, significant hypotensive and anaphylactoid effects of protamine have limited its clinical utility. Thus, due to its heparin binding and neutralization activities, BPI has potential utility as a substitute for protamine in heparin neutralization in a clinical context without the deleterious side-effects which have limited the usefulness of the protamines. The additional antibacterial and anti-endotoxin effects of BPI would also be useful and advantageous in post-surgical heparin neutralization compared with protamine.
Additionally, BPI protein products are useful in inhibiting angiogenesis due in part to its heparin binding and neutralization activities. In adults, angiogenic growth factors are released as a result of vascular trauma (wound healing), immune stimuli (autoimmune disease), inflammatory mediators (prostaglandins) or from tumor cells. These factors induce proliferation of endothelial cells (which is necessary for angiogenesis) via a heparin-dependent receptor binding mechanism. Angiogenesis is also associated with a number of other pathological conditions, including the growth, proliferation, and metastasis of various tumors; diabetic retinopathy, retrolental fibroplasia, neovascular glaucoma, psoriasis, angiofibromas, immune and non-immune inflammation including rheumatoid arthritis, capillary proliferation within atherosclerotic plaques, hemangiomas, endometriosis and Kaposi's sarcoma. Thus, it would be desirable to inhibit angiogenesis in these and other instances, and the heparin binding and neutralization activities of BPI are useful to that end.
Another utility of BPI protein products involves pathological conditions associated with chronic inflammation, which is usually accompanied by angiogenesis. One example of a human disease related to chronic inflammation is arthritis, which involves inflammation of peripheral joints. In rheumatoid arthritis, the inflammation is immune-driven, while in reactive arthritis, inflammation is associated with infection of the synovial tissue with pyogenic bacteria or other infectious agents. Many types of arthritis progress from a stage dominated by an inflammatory infiltrate in the joint to a later stage in which a neovascular pannus invades the joint and begins to destroy cartilage. While it is unclear whether angiogenesis in arthritis is a causative component of the disease or an epiphenomenon, there is evidence that angiogenesis is necessary for the maintenance of synovitis in rheumatoid arthritis. BPI has been shown to provide effective therapy for arthritis and other inflammatory diseases.
Three separate functional domains within the recombinant 23 kD N-terminal BPI sequence were discovered by Little et al., J. Biol. Chem. 269: 1865 (1994) [see also copending and co-assigned WO94/20128 (PCT/US94/02401); WO94/20532 (PCT/US94/02465) ;and WO95/19372 (PCT/US94/10427)]. These functional domains of BPI designate a region of the amino acid sequence of BPI that contributes to the total biological activity of the protein and were essentially defined by the activities of proteolytic cleavage fragments, overlapping 15-mer peptides and other synthetic peptides. Domain I is defined as the amino acid sequence of BPI comprising from about amino acid 17 to about amino acid 45. Peptides derived from this domain were moderately active in both the inhibition of LPS-induced LAL activity and in heparin binding assays, and did not exhibit significant bactericidal activity. Domain II is defined as the amino acid sequence of BPI comprising from about amino acid 65 to about amino acid 99. Peptides derived from or based on this domain exhibited high LPS and heparin binding capacity and were bactericidal. Domain III is defined as the amino acid sequence of BPI comprising from about amino acid 142 to about amino acid 169. Peptides derived from or based on this domain exhibited high LPS and heparin binding activity and were bactericidal. The biological activities of BPI functional domain peptides may include LPS binding, LPS neutralization, heparin binding, heparin neutralization or antimicrobial activity.
Of interest to the present application are the disclosures of the following references which relate to recombinant fusion proteins and peptides.
Shen, Proc. Nat'l. Acad. Sci. (USA), 281:4627 (1984) describes bacterial expression as insoluble inclusion bodies of a fusion protein encoding pro-insulin and .beta.-galactosidase; the inclusion bodies were solubilized with formic acid prior to cleavage with cyanogen bromide.
Kempe et al., Gene, 39:239 (1985) describes expression as insoluble inclusion bodies in E. coli of a fusion protein encoding multiple units of neuropeptide substance P and .beta.-galactosidase; the inclusion bodies were solubilized with formic acid prior to cleavage with cyanogen bromide.
Lennick et al., Gene, 61.103 (1987) describes expression as insoluble inclusion bodies in E. coli of a fusion protein encoding multiple units (8) of .alpha.-human atrial natriuretic peptide; the inclusion bodies were solubilized with urea prior endoproteinase cleavage.
Dykes et al., Eur. J. Biochem., 174:-411 (1988) describes soluble intracellular expression in E. coli of a fusion protein encoding .alpha.-human atrial natriuretic peptide and chloramphenicol acetyltransferase; the fusion protein was proteolytically cleaved or chemically cleaved with 2-(2-nitrophenylsulphenyl)-E-methyl-3'-bromoindolenine to release peptide.
Ray et al., Bio/Technology, 11:64 (1993) describes soluble intracellular expression in E. coli of a fusion protein encoding salmon calcitonin and glutathione-S-transferase; the fusion protein was cleaved with cyanogen bromide.
Schellenberger et al., Int. J. Peptide Protein Res., 41:-326 (1993) describes expression as insoluble inclusion bodies of a fusion protein encoding a substance P peptide (11a.a.) and .beta.-galactosidase; the inclusion bodies were treated with chymotrypsin to cleave the fusion protein.
Hancock et al., WO94/04688 (PCT/CA93/00342) and Piers et al. (Hancock), Gene, 134:7 (1993) describe (a) expression as insoluble inclusion bodies in E. coli of a fusion protein encoding a defensin peptide designated human neutrophil peptide 1 (HNP-1) or a hybrid cecropin/mellitin (CEME) peptide and glutathione-5-transferase (GST); the inclusion bodies were: (i) extracted with 3% octyl-polyoxyethylene prior to urea solubilization and prior to factor X.sub.a protease for HNP1-GST fusion protein or (ii) solubilized with formic acid prior to cyanogen bromide cleavage for CEME-GST fusion protein; (b) expression in the extracellular supernatant of S. aureus of a fusion protein encoding CEME peptide and protein A; (c) proteolytic degradation of certain fusion proteins with some fusion protein purified; and (d) proteolytic degradation of other fusion proteins and inability to recover and purify the fusion protein.
Lai et al., U.S. Pat. No. 5,206,154 and Callaway, Lai et al. Antimicrob. Agents & Chemo., 37.1614 (1993) describe expression as insoluble inclusion bodies of a fusion protein encoding a cecropin peptide and the protein encoded by the 5'-end of the L-ribulokinase gene; the inclusion bodies were solubilized with formic acid prior to cleavage with cyanogen bromide.
Gamm et al., Bio/Technology, 12:1017 (1994) describes expression as insoluble inclusion bodies in E. coli of a fusion protein encoding a human parathyroid hormone peptide and a bacteriophage T4-encoded gp55 protein; the inclusion bodies (6% wt/vol.) were treated with acid to hydrolyze the Asp-Pro cleavage site.
Kuliopulos et al., J. Am. Chem. Soc., 116:4599 (1994) describes expression as insoluble inclusion bodies in E. coli of a fusion protein encoding multiple units of a yeast .alpha.-mating type peptide and a bacterial ketosteroid isomerase protein; the inclusion bodies were solubilized with guanidine prior to cyanogen bromide cleavage.
The above-references indicate that production of small peptides from bacteria has been problematic for a variety of reasons. Proteolysis of some peptides has been particularly problematic, even where the peptide is made as a part of a larger fusion protein. Such fusion proteins comprising a carrier protein/peptide may not be expressed by bacterial host cells or may be expressed but cleaved by bacterial proteases. In particular, difficulties in expressing cationic antimicrobial peptides in bacteria have been described by Hancock et al. WO94/04688 (PCT/CA93/00342) referenced above, due in their view to the susceptibility of such polycationic peptides to bacterial protease degradation.
There continues to exist a need in the art for new recombinant products and in particular, a need for methods for recombinant production of BPI-derived peptides useful as antimicrobial agents (including anti-bacterial and anti-fungal agents), as endotoxin binding and neutralizing agents, and as heparin binding and neutralizing agents, including agents for neutralizing the anticoagulant effects of administered heparin, for treatment of chronic inflammatory disease states, and for inhibition of normal or pathological angiogenesis.